Clinical practitioners have developed standard views for 2-D ultrasound imaging which remove much of the operator and view variability and speed up image acquisition and review. This is particularly true for trans-thoracic echocardiography, where there are only a few "windows" past the ribs and lungs which allow good image acquisition. The echocardiology standard views are illustrated in FIGS. 1a-1c and include the parasternal long axis view (FIG. 1a), the parasternal short axis view (FIG. 1b) and the apical 4-chamber view (FIG. 1c). The operator typically moves through a sequence of such standard views, putting the ultrasound transducer on the patient in standard places and with standard orientations. Thereafter, slight adjustments of the transducer position are made by the operator, based upon the displayed image.
The provision of standard views is highly useful to the practitioner as it enables recognition of differences between subsequent standard views, without requiring the practitioner to initially determine from what aspect ratio the view has been derived. See U. S. Pat. 5,315,999 to Kinicki et al., assigned to the same assignee as this Application, for further discussion re: preset imaging modes and parameters therefor.
Notwithstanding the obvious usefulness of 2-D imaging, such systems provide only a limited number of views of many organs, e.g., the heart. Recently, 3-D ultrasound systems have been introduced which acquire data for many different views from a single placement of a transducer on the patient. In such case, the view may be a 2-D slice, a 3-D rendering or another view derived from the data. A potential advantage of 3-D view acquisition is that the view can be optimized for the anatomy, rather than being fixed relative to the transducer. To accomplish 3-D imaging, a 3-D data set of image echo values is accumulated and subsequently processed to provide the desired view presentation. The process of acquiring a 2-D view from a 3-D data set is well known and need not be further elaborated.
As indicated above, FIGS. 1a-1c illustrate schematic showings of ultrasound heart images, given a positioning of the ultrasound transducer at one of the: apical, parasternal, suprasternal or subcostal imaging positions. Such views are: "standard" and provide showings of the long-axis view (FIG. 1a), the short axis view (FIG. 1b) and the 4-chamber view (FIG. 1c). The provision of such standard views enables ready diagnosis by the practitioner. As is known, however, certain features of the heart cannot be imaged using 2-D imaging systems. More specifically, features like face-on views of the pulmonary valve (shown in FIG. 2a in its open state), the aortic valve (shown in FIG. 2b in its closed state), and the mitral valve (shown in FIG. 2c in its closed state) cannot be directly imaged. To provide such views, the user must employ a 3-D ultrasound system.
Present implementations of 3-D ultrasound systems offer essentially only two methods for selecting a view. The first method provides a view which is derived from a simple fixed orientation relative to the transducer, such as an orthogonal 2-D slice. A second method is totally arbitrary and under explicit manual control of the operator. Such control is complicated and tedious due to the many parameters to be specified. For instance, many arbitrary views are constructed in an iterative, trial and error fashion, long after data acquisition. Some of the parameters which require operator adjustment and control are: orientation, viewpoint, bounding region, magnification, rendering technique, etc., etc.
Accordingly, the derivation of such a 3-D view is a slow and tedious process. Therefore, it is usually performed on an "off-line" computer system so as to avoid occupying a valuable ultrasound system during a period when it could be in use deriving further patient diagnostic views.
Therefore, a need exists for a clinical ultrasound imaging system which reduces the complexities facing the operator when obtaining a desired anatomical view from a 3-D data set. Further, certain 2-D anatomical views are diagnostically useful but cannot be readily obtained from standard ultrasound transducer imaging positions. The automatic availability of such views from 3-D data sets, on a real time basis, would be extremely useful from a diagnostic point of view.